1. Technical Field
The present invention is related to an objective lens for an endoscope and an endoscope.
2. Description of the Related Art
Conventionally, insertion type endoscopes have been available in a medical field, for inserting an elongated insertion unit with a built-in imaging device at the tip portion thereof from the nose, mouse, etc. to pick up images of the interior of a body cavity. In addition, capsule type endoscopes also have been employed. In such capsule type endoscopes, a subject swallows a capsule that houses an imaging device and the like therein, and then the capsule picks up images of the interior of a body cavity while naturally moving through the inside of the subject. In these endoscopes, there is demand for the diameters of insertion units and the sizes of capsules to be decreased so as to reduce the burden on subjects. Accompanying these demands, objective lenses for endoscopes to be mounted on endoscopes are also being required to be miniaturized.
Miniaturized objective lenses for endoscopes have been proposed, in which the number of lenses that constitute the entire system is extremely reduced to two or three. For example, Patent Documents 1 through 4 (Japanese Unexamined Patent Publication No. 2009-297401, Japanese Patent No. 4843121, Japanese Patent No. 3758801, and Japanese Patent No. 3450543) disclose objective lenses for endoscopes constituted by a first lens group composed of a single negative lens; a stop; and a second lens group composed of one or two lenses, having a positive refractive power; in this order from the object side.